*Excludes Observations that spanned multiple years
| Pre 1970 | 222 |
|---|---|
| 1970 | 27 |
| 1971 | 15 |
| 1972 | 51 |
| 1973 | 64 |
| 1974 | 73 |
| 1975 | 36 |
| 1976 | 24 |
| 1977 | 28 |
| 1978 | 13 |
| 1979 | 28 |
| 1980 | 32 |
| 1981 | 37 |
| 1982 | 41 |
| 1983 | 33 |
| 1984 | 67 |
| 1985 | 68 |
| 1986 | 41 |
| 1987 | 56 |
| 1988 | 24 |
| 1989 | 64 |
| 1990 | 89 |
| 1991 | 113 |
| 1992 | 106 |
| 1993 | 116 |
| 1994 | 139 |
| 1995 | 196 |
| 1996 | 178 |
| 1997 | 141 |
| 1998 | 218 |
| 1999 | 248 |
| 2000 | 212 |
| 2001 | 518 |
| 2002 | 375 |
| 2003 | 233 |
| 2004 | 343 |
| 2005 | 177 |
| 2006 | 281 |
| 2007 | 244 |
| 2008 | 298 |
| 2009 | 340 |
| 2010 | 313 |
| 2011 | 260 |
| 2012 | 544 |
| 2013 | 789 |
| 2014 | 489 |
| 2015 | 509 |
| 2016 | 393 |
| 2017 | 407 |
| 2018 | 245 |
| 2019 | 276 |
| 2020 | 488 |
| 2021 | 380 |
| 2022 | 227 |
| 2023 | 6 |
| 2024 | 13 |
| 2025 | 3 |
| Total | 10951 |